Blue tits nesting query - have they all just left?

Hello,

It has been just over three weeks since I think the baby birds hatched in the nesting box. The parents have been diligently feeding them and I have seen them coming and going constantly.

2 days ago was the last time I heard or saw anything. From the box or the parents. Should I be concerned, or will they have all just left?

I am very hesitant to actually look in the box as I am really sensitive and would be be really upset to find dead babies I have been hearing for the last three weeks :/